Generally, cells are cultured in vitro in either suspended cultures or adherent cultures. In suspended culture, cultured cells are grown while suspended in a growth media. Cell cultures grown in suspension are typically derived from cell types that naturally live in suspension without being attached to a surface or to one another. In adherent cell culture environments, cultured cells adhere to surfaces (e.g., the surfaces of a culture vessel) and/or to one another as a support for cell growth.
Examples of suspended cells that can be cultured in vitro include blood cells, lymphocyte cells, and the like. Examples of adherent cells that can be cultured in vitro include epithelial cells, hematopoietic cells, mast cells, neurocytes, hepatocytes, hepatic parenchymal cells, bone marrow cells, osteoblasts, fibroblasts, epidermal cells, many stem cell types, and the like.
When adherent cells are ready for harvesting, chemical means such as enzymes (e.g., collagenase) and/or physical means such as glass capillary colony cutters have generally been used to separate the cells from the growth surface and/or to separate the cells from one another. Harvesting of cells grown in suspension or suspended adherent cells is typically performed by filtration, centrifugation, antibody processes, beads, pipetting, and the like. However use of chemicals, enzymes, and/or physical means to separate cultured cells can damage the cells.
In some cases, different types of cells are mixed in culture. For example, stem cells may be cultured with feeder cells, or stimulating cells (e.g., antigen presenting cells and a cancer cell line) may be co-cultured. In cases where mixed cultures are concerned, separation of the cells in the mixed culture can be additionally complicated and require additional physical and/or chemical processes, such as filtration, centrifugation, antibody, or beads. Again, these processes can damage the cells.